(1) Field of the Invention
The present invention relates to devices which perform processing on images of objects, and in particular to devices which perform processing on shadows.
(2) Description of the Related Art
Recently, image processing methods using shadows have been widely performed. For example, Non-patent Reference 1 has proposed an approach for estimating the distribution of light from a light source of real lighting based on the luminance distribution in a cast shadow which is a “shadow” generated by a material body which is an object having a known shape. This approach is derived from the fact that the relationship between the light source, the object, and the shadow can be represented as a geometrical and optical model. When this concept is applied to an environment about which light source information is known, it is possible to estimate the three-dimensional shape of an object based on the shadow.
In addition, in image processing, when the luminance is low in a portion of an image due to inverse light or a shadow, a shadow correction process for correcting only the luminance of the shadow area is performed to provide a beautiful image.
Here, a “shadow” appears when light reaches a solid, and contains an “attached shadow” and a “cast shadow”. An “attached shadow” appears on the solid itself depending on the angle of incidence light, and a “cast shadow” appears on a plane or on another solid when light is blocked by the former solid.
Since the Non-patent Reference 1 is a method for estimating a light source distribution based on such shadow area only, it is obvious that no accurate estimation can be performed in the case where the processing is performed based on a judgment that an attached shadow area is a cast shadow area.
In addition, in the case of shadow correction process, an attached shadow area is an element providing a stereoscopic vision of an object. Thus, it is desirable that such correction is made for the cast shadow area only, and no processing is performed on the attached shadow area.
For this, it is very important to classify shadow areas into attached shadow areas and cast shadow areas.
In order to classify shadow areas into attached shadow areas and cast shadow areas, Non-patent Reference 2 generates a linearized image which is an image obtainable in an ideal state where no specular reflection occurs, using an image of an object lighted by light sources in various directions, and classifies the shadow areas based on the linearized image.
Non-patent Reference 1: “Buttai no inei ni motozuku kogen kankyo suitei (Illumination Distribution from Shadows), Computer Vision and Imaging Media, the Journal of The Institute of Electronics, Information and Communication Vol. 41, No. SIG10 (CVIM1), pp. 31-40, 2000, Imari Sato, Yoichi Sato, Katsushi Ikeuchi.Non-patent Reference 2: “Kogaku gensho no bunrui ni motozuku gazo no senkeika (Photometometric Linearization based on Classification of Photometric Factors)”, Computer Vision and Imaging Media, the Journal of The Institute of Electronics, Information and Communication, Vol. 44, No. SIG5 (CVIM6), pp. 11-21, 2003, Yasunori Ishii, Kohtaro Fukui, Yasuhiro Mukaigawa, Takeshi Shakunaga.